Axle question 1/2 and 3/4 ton

[Branktm]

I am in the middle of a frame off restore on my 76 K15. Frame actually goes off to powder coat in a week. I have a 6 inch RC suspension kit being shipped this week, and the plan was 37s on 15inch rally wheels, (85% sure on the wheels, 100% sure on the 37s)
When searching for an engine rebuilder for the 350 i came across a 76 K20 with a fresh motor for cheaper than a rebuild. So i bought it as it came with many other takeoffs i could use. I checked my 1/2 ton rear end and it has 3.73 gearing which wont do with the lift and tire combo. My question is, when i dive into the 3/4 ton which i was told is geared low, is it possible to use a rear end from a 3/4 ton and convert it to a 6 lug vs 8 lug? I know this is a dumb question, but i dont know any better. Trying to decide what to do, and no i have no idea what model rear ends they are. Need to dive in more, i want to keep 6 lug because of the rally wheel route. If i can use 3/4 ton axle with 6 lugs great, (if gearing is right) if not i gotta regear the 1/2 axle. Either way 3/4 ton will be parted out for 2 weeks before going to a pick a part most likely. Thanks!

 

[C10MixMaster]

I am in the middle of a frame off restore on my 76 K15. Frame actually goes off to powder coat in a week. I have a 6 inch RC suspension kit being shipped this week, and the plan was 37s on 15inch rally wheels, (85% sure on the wheels, 100% sure on the 37s)
When searching for an engine rebuilder for the 350 i came across a 76 K20 with a fresh motor for cheaper than a rebuild. So i bought it as it came with many other takeoffs i could use. I checked my 1/2 ton rear end and it has 3.73 gearing which wont do with the lift and tire combo. My question is, when i dive into the 3/4 ton which i was told is geared low, is it possible to use a rear end from a 3/4 ton and convert it to a 6 lug vs 8 lug? I know this is a dumb question, but i dont know any better. Trying to decide what to do, and no i have no idea what model rear ends they are. Need to dive in more, i want to keep 6 lug because of the rally wheel route. If i can use 3/4 ton axle with 6 lugs great, (if gearing is right) if not i gotta regear the 1/2 axle. Either way 3/4 ton will be parted out for 2 weeks before going to a pick a part most likely. Thanks!

pretty sure the axle on the 3/4 that sticks through the wheel is way bigger than the hole in the 1/2 ton wheel . No go.

 

[eskimomann209]

I’m not too certain about the axle you have with the 8 lug. Take some pics of both and post them so we know what you’re working with.

 

[75gmck25]

Many of the 3/4 tons have 4.10 gears, and the FF axle is common on higher GVW trucks. Look at the axle center hubs. If the center hub sticks out it is a 14 bolt Full Floating axle, which is the strongest axle GM used in that timeframe.

if you are running 37’s just for looks it might not be worth it to swap, but for actual off-roading the 14 FF would be a much better axle.

Bruce

 

[Craig 85]

I did an axle swap on my '79 K15. I had 3.08 gears and a peg leg rear. In my case, since I was going to change wheels anyways, it was cheaper doing the axle swap. I ended up with 4.10's, a limited slip rear and bigger brakes. I picked up the pair of axles for $400.

GM did make 14 bolt semi float rear ends in 6 lug. Usually they are found on GMT-400's that are labelled light duty 2500's. You would have to change the spring and shock mounts. The problem with those most are 3.73's and I would bet few are 4.10's.

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[BKING33]

There is no way to convert those to 6-lugs. Till you price out the cost of new gear sets and good locker, u might consider sticking with 8-lugs. I had a 6 lug truck with 36" tires and 4.10s. Would not recommend 6-lugs with 37s they put alot of stress on axles and gears. I actually broke a 12-bolt ring gear on mine with the 36's on.

 

[Branktm]

dang, kind of what i thought, sounds like taking the 3/4 axles is the way to go, just really wanted the rally wheel look. Thank you all for your help, i got some decisions to make.

 

[RecklessWOT]

No idea who makes them, but I have seen wheels that look like factory rallye wheels but have weird backspacing, or are larger than 15" etc. You might look around and find ones that are 8 lug? If not, maybe you can get some with different backspacing and run adapters in the same way someone would use wheel spacers.

I have also seen people run wheels from mid 90s dodge rams or full size vans. They aren't identical to rallye wheels, but they have a similar style. Any GM guy will notice in 2 seconds that they're not rallye wheels, but they still give off the same vibe if that makes sense


edit: a quick google search just came up seeming like nobody makes an aftermarket rallye wheel with 8 lugs.

I can't get a picture to link, but click on this to see those dodge wheels

 

[Nonstop]

https://www.sneveysoffroad.com/gm_14_bolt_ff_6_lug_conversion_kit

You can do it...but it looks pricey! I would suggest sticking with the 8 lug set up.

 

[Craig 85]

just really wanted the rally wheel look.

This is always an option for 8 lug rallys. GMT-400 (88-99). Photo 2 & 3 are on a widened wheel. If you want a beefier looking hub, use '99-10 center caps (photo #3).

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[AuroraGirl]

This is always an option for 8 lug rallys. GMT-400 (88-99). Photo 2 & 3 are on a widened wheel. If you want a beefier looking hub, use '99-10 center caps (photo #3).

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IS THAT... A FORD????

Im joking, nice truck regardless. ALSO AWESOME WHEELS. Are they yours?

 

[Craig 85]

IS THAT... A FORD????

Im joking, nice truck regardless. ALSO AWESOME WHEELS. Are they yours?

That's a 68-72 Chevy truck and no not my wheels. I had thought of this for my truck, but I probably would have had more money in them than my alloy wheels cost since I would have had to widen them to 10".

 

[AuroraGirl]

That's a 68-72 Chevy truck and no not my wheels. I had thought of this for my truck, but I probably would have had more money in them than my alloy wheels cost since I would have had to widen them to 10".

OH damn, not the first time i mistook the rear end view of a ford for a chevy from that era.

And holy cow, 10 inch wheel. You must run some nice big rubber on your truck.

 

[Grit dog]

dang, kind of what i thought, sounds like taking the 3/4 axles is the way to go, just really wanted the rally wheel look. Thank you all for your help, i got some decisions to make.

Check out Detroit steel wheels. You can do a rally wheel look in 8 lug

18-22” dia, 9-14” wide in a couple different wheel styles.

 

[Craig 85]

OH damn, not the first time i mistook the rear end view of a ford for a chevy from that era.

And holy cow, 10 inch wheel. You must run some nice big rubber on your truck.

Nothing too big 305/70R16 (33 x 12.50 roughly).

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